Obstructive sleep apnea (OSA) in individuals with Down syndrome is associated with multiple morbidities: systemic and pulmonary hypertension, glucose intolerance, cardiovascular and cerebrovascular disease, and behavioral problems. The prevalence of OSA in this population is very high, with estimates ranging between 55-97%. Currently, an overnight polysomnogram (sleep study) is the gold-standard diagnostic test for patients with Down syndrome. Yet, this testing is cumbersome, poorly tolerated by these children, costly, and not widely available around the country. In this pilot project, we propose to identify predictive factors for OSA in persons with Down syndrome. By doing so, we will provide the foundation for establishing an effective, reliable, and user-friendly tool to screen for OSA in individuals with Down syndrome without needing a polysomnogram. We will enroll 100 subjects, ages 3-18 years, who already participate in the Down syndrome program at Children's Hospital Boston. For each patient, we will collect subjective and objective measurements using validated parental survey instruments, standardized physical exams, lateral cephalograms, 3D-digital photogrammetry, and urine samples. Afterwards, all participants will undergo standardized polysomnography at the Children's Hospital Boston Sleep Laboratory where objective measurements will be collected on OSA. We will analyze which combination of our assessment methods predicts OSA as ultimately determined by polysomnography. Our screening tool will allow physicians to avoid ordering polysomnograms for those individuals with Down syndrome at lowest risk of OSA. Further, those patients with Down syndrome and clear predictors for OSA can proceed directly toward adenotonsillectomy, the current treatment.